Traditional laminates used for printed circuit mainly utilize brominated flame retardants to achieve flame retardancy, in particular utilize tetrabromobisphenol-A epoxy resin which has good flame retardancy but can produce hydrogen bromide gas when burning. In addition, in recent years, carcinogens such as dioxins, dibenzofurans and others have been detected in the combustion products of wastes of electrical and electronic equipments containing halogen such as bromine, chlorine and the like, and thus the use of brominated epoxy resin is limited. On Jul. 1, 2006, two environmental protection directives of the European Union, “Directive on the Waste Electrical and Electronic Equipment” and “Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment” were officially implemented. The development of halogen-free flame retardant copper-clad laminates has become a hot topic in the related industry field, and each copper-clad laminate manufacturer has launched their own halogen-free flame retardant copper-clad laminate in succession.
With the development of high-speed and multi-functionalization of information processing of electronic products, the frequency applied is increasing. In addition to a higher demand for thermal resistance of laminate materials, there is also a demand that the dielectric constant and the dielectric loss value become lower and lower, and thus reducing Dk/Df has become a hot topic pursued by the practitioners in substrate industry. Traditional FR-4 materials mainly utilize dicyandiamide as a curing agent. This curing agent has a reactive tertiary amine and has good processing operability, but since its C—N bond is weak and easy to crack at a high temperature, resulting in a lower thermal decomposition temperature for the cured product, it cannot meet the demand for thermal resistance during the lead-free manufacturing process. In this background, with the wide implementation of the lead-free technology in 2006, phenolic resin began to be used as an epoxy curing agent in the industry. Phenolic resin has benzene ring structures with high density, and thus the thermal resistance of a cured system of phenolic resin and epoxy resin is excellent, but the dielectric properties of the cured product have a trend of being worse.
CN 101914265A discloses a halogen-free phosphorus-containing flame retardant high-frequency epoxy resin composition. In the resin composition of the invention, conventional brominated difunctional epoxy resin is substituted by multifunctional epoxy resin; conventional dicyandiamide is substituted by linear phenolic resin serving as a curing agent. The epoxy resin composition consists of benzoxazine epoxy resin, tetraphenol ethane epoxy resin, DOPO modified phenolic resin, alkyl modified phenolic resin, imidazole accelerating agent, inorganic filler, inorganic auxiliary flame retardant filler and the like. The bonding sheet and the copper-clad plate, which are prepared from the epoxy resin composition and are used for a printed circuit board, have environmentally-friendly flame retardancy and excellent dielectric performance. But the bonding sheet and the copper-clad laminate have a water absorption being up to 0.3%-0.4%, and thus can absorb moisture easily resulting in delamination in the subsequent process for preparing PCB, and the dielectric properties thereof are common, therefore it is difficult to meet the requirements for development of high frequency in electronic signal transmission and high-speed in information processing in the industry of printed circuit copper clad laminate.